Joint replacement surgery is performed on patients with degenerative joint diseases, such osteoarthritis and arthrosis, with the goals of relieving pain and restoring function, thus improving the quality of life for the patient. Although joint replacement surgery is exceedingly common, with approximately 700,000 knee replacement procedures performed annually in the U.S., it has been reported that a significant portion of patients (approximately one in five) are not satisfied with the results of their surgery. While this may be due to a number of factors, such as patient expectations, it is suspected that surgical technique related factors may play an important role in the number of cases that have less than optimal outcomes. In fact, several clinical studies have indicated that soft tissue related factors, such as instability and stiffness, are the leading cause for failure of total knee arthroplasty (TKA).
The act of achieving the appropriate soft-tissue tension and balance in joint replacement surgery is still regarded as somewhat of an art form by surgeons. This is partly because the act of assessing the tension in the soft tissues that surround a joint is largely a subjective process where the surgeon manually applies forces and moments to one side of the joint and observes the opening or compliance of the joint under the applied force by feel and by eye. Thus the assessment of soft tissue tension may vary depending on the surgeon performing the assessment, how they were trained, hold the limb by hand, and this may also vary from day to day, or from their left to right hand.
The standard of care in joint replacement surgery today is to use manual instrumentation which includes alignment rods, cutting blocks, provisional trial implants, and tensioning tools such as laminar spreaders or specifically designed manual spreaders. Robot and computer-assisted surgery systems have been introduced in the late 90's and have been increasing in development and use. However, most of systems currently on the market only partially address the soft tissue tensioning and balancing problem. Moreover, these systems still require a large number of instruments and provisional trial components to be available in the operating room.